The following is a sample script that sets a Preference registry value in a GPO, then compares that same value to all of the GPO's linked in the same domain. If the value is not already set in a linked GPO, the new GPO is linked to that domain as well.

You can copy and paste the following text into a .ps1 file and run it, given a few modifications (the comments denote where you should replace my example names with your own GPO and domain names). The # symbols act like comments in the .ps1 file so you don't need to worry about them being run or printing out.

Hope this helps!

 LiliaG, Group Policy PM

## The following script sets a Preference registry value in a GPO, then compares that same value to all of the GPO's linked in the same domain
## it depends on being opened from the Active Directory provider shortcut to the PowerShell console, or navigating to that AD provider first

# necessary for any work with group policy cmdlets
import-module grouppolicy

# create new GPO. Replace "GPDEMO" with the name of your choice

new-GPO GPDEMO

# set the variable $key to the string value of the registry key to be set

$key = 'HKEY_CURRENT_USER\Software\Adobe\Acrobat Reader\8.0\InstallPath'

# set GP Pref Registry Value

Set-GPPrefRegistryValue -Name GPDEMO -Context User -Key $key -ValueName (Default) -Value "C:\ProgramFiles(x86)\Adobe\Reader8.0\Reader" -Type String -Action Create

#get all GPO's linked in the domain you choose
#first step is to get the domain object you want

#Replace <your domain here> with the NetBIOS, DNS, SID, or Distinguished Name of the domain

$domain = get-ADDomain -Identity <your domain here>

# enter "get-ADDomain -?" for help

# the next step gets all the GPO's currently linked to that domain and extends the attributes to include the GUID of those GPO's

# the second portion of this line is important for parsing the resulting list of GPOs, do not skip it! You must get the " -properties Name " in order to refer to the GPO's by their GUID.

$GPOList = $domain.AppliedGroupPolicies | %{Get-ADObject $_ -Properties Name}

# sets up the variable to be compared against the other GPO's in the domain

$preference = get-GPPrefRegistryValue -Name GPDEMO -Context User -Key $key -ValueName (Default)

# warning: this does not check to see if there are other GPO's linked to the domain, this loop will break if there is only one GPO linked in the domain

# loop through

$i = 0
$redundantSetting = 0

while ($i -lt $GPOList.count) {

$CompareGPO = get-GPO -GUID $GPOList[$i].Name

# report out equality

if (($preference.Value).equals($comparePref.Value))
  {
    "Equal!"
     $redundantSetting++
  } else {
     "Not Equal!"
  }

# reset the loop

$comparePref = 0
$i++
}

# if none of the GPO's linked to the domain have the setting, link this new GPO. Otherwise, do not link it.

if ($redundantSetting -gt 0)
  {
     new-GPLink GPDEMO -Target $domain
  } else {
    "Not linking a redundant GPO"
  }

Now, when I detect a redundant setting, I just print something out to the screen. You can do something more interesting, like write to a file, trigger another script, send an email, etc. In fact, I hope you do! Let me know what you do with this script, how you improve it, if/how you use it, or if it causes you any trouble.